The invention relates generally to a system and process for manufacturing high transition temperature (Tc) oxide superconductor wire. The invention more particularly relates to a system and apparatus for coating, winding and heat treating high Tc oxide superconductor wire.
Many applications of the high Tc oxide superconductors requires forming the superconductor into a wire. Current processes include forming a precursor of the oxide superconductor or the oxide superconductor itself into a wire and heat treating the wire to obtain an oxide superconductor wire. Current developments in high Tc oxide superconductor processing have resulted in the manufacture of increasingly longer lengths of oxide superconductor wire with acceptable current carrying capacity. The loading and unloading of oxide superconductor wire is an important step in the processing of the wire, in particular, to move the wire between wire deforming steps, such as pressing and rolling, and oxide superconductor phase-forming steps, such as sintering and annealing. The prior art wire deforming step is typically carried out by feeding the wire from a conventional spool through the deforming step and taking up the deformed wire onto a second conventional spool. Long lengths of wire can be efficiently wound onto the spool. However, the conventional spool is not readily adaptable for use in furnaces and results in inefficient use of furnace space. Further, the wire tends to sag and become distorted (wavy) because of the coiled form of the wire on the spool. Lastly, the multiple overlapping windings on the spool do not permit efficient oxidation and phase transformation of the oxide superconductor.
A further disadvantage to winding the oxide superconductor wire prior to heat treatment is that overlapping contact between portions of the wire results in diffusion bonding of the wire to itself and the mandrel, thereby degrading superconducting properties and preventing the unspooling of the heat treated wire. Silver is commonly used as a protective cladding for the oxide superconductor, in particular because the cladding itself is electrically conductive and does not prevent oxygen diffusion to the oxide superconductor. However, even the silver cladding will diffusion bond to other portions of the silver-cladded wire which are in contact during heat treatment.
U.S. Pat. No. 5,140,006 discloses a method and apparatus for coating a silver-cladded oxide superconductor wire with a diffusion-inhibiting material and taking up the coated wire onto a spool. Rare earth oxides are specifically disclosed as a desirable diffusion inhibiting material and no disclosure of the desirability of removing the material after treatment is disclosed.
It is the object of the present invention to efficiently process high-Tc superconducting oxide wire by increasing the simplicity and efficiency of the method used to load and unload wire during processing, by reducing adhesion of the wire to itself and by maximizing the use of furnace space during heat treatment.
In one aspect of the invention, an oxide superconducting wire is prepared by providing an oxide superconductor wire and applying an isolating layer to an external surface of the wire. The isolating layer includes an isolating material and a porosity-inducing component. The coated wire is heated so as to induce porosity into the isolating layer, thereby obtaining a removable porous isolating layer. The coated oxide superconductor wire is then further processed, as required.
In another aspect of the invention, an oxide superconducting wire is prepared by providing an oxide superconductor wire and applying an isolating layer to an external surface of the wire. The isolating layer includes an isolating material and a porosity-inducing component. The coated wire is wound onto a reel in a spiralling manner, such that each turn of the spiral is in alignment with the preceding turn of the spiral along an axis perpendicular to the axis of winding. The coated oxide superconductor wire is then further processed, as required.
By xe2x80x9coxide superconducting wirexe2x80x9d, as that term is used herein, it is meant a wire at all stages of manufacture, but which can ultimately be processed into a superconductor wire. Therefore, precursor wires, which are converted into an oxide superconductor wire is deemed a superconductor wire for the purposes of the invention. Likewise, a wire which is only partially converted into the oxide superconductor, or which contains the oxide superconductor but requires further processing to optimize the electrical properties are likewise deemed an oxide superconductor wire for the purposes of the invention.
By xe2x80x9cin alignmentxe2x80x9d as that term is used herein, it is meant that each turn of the spiral is in alignment with and substantially completely overlapping with the previous turn of the spiral, such that the wound wire takes on a substantially two-dimensional appearance. The wound wire is similar in appearance to a wound cassette reel of audio tape.
By xe2x80x9cporosity-inducing componentxe2x80x9d as that term is used herein, it is meant a primarily carbon-containing material which is capable of combustion or thermal decomposition with very little or no residues. The space formerly occupied by the component, after such decomposition, provides the requisite porosity.
The oxide superconducting wire prepared by the present invention possesses superior isolation of successive wire layers and the spool and is capable of easy removal of the layer for further wire processing.